The overall objective of this project is to study the interface of the placenta with its environment, with particular emphasis on the nature and formation of surface macromolecules on human syncytial trophoblast, the cell biology of the synthesis of this material, and the localized variation in surface properties in relation to protein binding. Evidence of synthesis by trophoblast is being studied using in vitro exposure of human and rhesus monkey placental villi to tritiated amino acids, sugars and in certain cases to sugar nucleotides. The effects of prior enzyme digestion on the in vitro binding of protein tracers is also being studied. BIBLIOGRAPHIC REFERENCES: Nelson, D.M., C.H. Smith, A.C. Enders and T.M. Donohue, 1976. The asymmetric distribution of acidic components on the human placental syncytial trophoblast surface membrane: a cytochemical and analytical study. Anat. Rec. 184: 159-182. Enders, A.C., W.A. Wimsatt and B.F. King, 1976. Cytological development of yolk sac endoderm and protein absorptive mesothelium in the little brown bat, Myotis lucifugus. Am.J. Anat. 146:1-30.